Many high-efficiency furnace designs employ a heat exchanger assembly including several serpentine heat exchangers. Hot exhaust gases from a burner associated with a particular heat exchanger travel through the serpentine path while an airstream to be warmed is forced over the heat exchanger. The airstream is thereby warmed as heat is extracted from the exhaust gas.
The heat exchanger is typically fastened to one or more metal plates that serve to mechanically support the heat exchanger assembly and to guide the airstream being warmed by the assembly. It is essential that the joints between the several heat exchangers and the one or more metal plates be well sealed to prevent exhaust gas from entering the airstream.